Field of Invention
The invention relates to an apparatus for adjusting and/or calibrating a multi-camera module having a plurality of cameras. Furthermore, the invention relates to the use of such an apparatus for adjusting and calibrating a multi-camera module as well as a method for adjusting and/or calibrating a multi-camera module having a plurality of cameras.
Brief Description of Related Art
Multi-camera modules are known in many different configurations and for various applications. Such modules comprise a plurality of cameras, often two cameras, which are distanced from each other by a stereo basis. The cameras of the multi-camera module capture an observation field made up of slightly different viewing directions or respective angles and capture together stereoscopic image data of the observation field, from which 3D data can be obtained.
Multi-camera modules are used, for example, in medical technology (3D endoscopes), in automobile technology (distance stereo cameras) or in the field of multi-media (3D cameras).
Some multi-camera modules comprise two or more completely separate camera modules. It is also known to design the imaging optics as separate components only, wherein the image sensors are combined, for example, into one assembly. The image sensors can thereby be arranged on separate components, for example separate printed circuit boards, or can also combined on one component, that is, for example, a common printed circuit board or die. There are modules in which the optics are combined in one component. Such systems are also called “one systems.” Multi-camera modules can also be equipped with cameras or imaging optics, which capture different viewing angles, which have e.g. different focal lengths. With such modules, a very fast zoom is possible by switching from one camera to the other. In general, a trend is observed towards smaller camera systems having a smaller stereo basis.
In multi-camera modules, it is necessary to align the two individual cameras relative to each other. This necessity pertains to the alignment of the image sensors and/or to the alignment of the respective imaging optics. It is possible to align the cameras with respect to each other with parallel optical axes in that objects lying in infinity are detected by all cameras at the same pixel position. It is also possible to adjust the cameras to a finitely far away object so this object at a finite distance is detected by all cameras at the same pixel position. In this case, the optical axes of the cameras intersect at a finite distance.
For aligning the cameras, test systems for multi-camera modules are known in which real objects are used as test structures (often also referred to as test charts) at different finite distances, in order to adjust or to calibrate the cameras of the multi-camera module with respect to each other. Such a test system is known for example from Luo et al., Pub. No. US 2014/0118503 A1. Test structures are observed at two different finite distances. The two individual cameras are aligned with respect to each other in an iterative process.
However, for exact alignment of the cameras of a multi-camera module around all six axes, a finite distance measurement is not sufficient. A suitable combination of a measurement at finite distance and a measurement at infinite distance should be carried out in order to determine all six degrees of freedom separately from each other and in order to be able to correspondingly align the cameras.
Multiple large distances between the test sample and a test structure are used for the approximately infinite measurement. The distance between the test sample and the test structure is thus selected very large compared to the focal length of the test sample. However, such a structure needs a lot of space.
The sequential measurement processes also used multiple times, in which measurements are performed at different distances, require a long measurement time, which is also undesirable. A test system, in which individual measurements are performed sequentially with different measurement distances, i.e. in succession temporally, is known for example from Kazunari et al., JP 05 589 823 B2. In the apparatus known from this document, a test structure lying in infinity is simulated with the help of a collimator. A test structure at a finite distance is provided at a second separate measurement location. The test sample is placed on a rotating table and, depending on the position of the table, is subjected either to a finite or an infinite measurement.
It is an object of the invention to provide an apparatus as well as a method for adjusting and/or calibrating a multi-camera module as well as the use of such an apparatus, wherein the adjustment and/or calibration of the multi-camera module should be precise and efficient.